This invention relates to filtering devices, and, more particularly, to a filter for removing impurities from hot melt adhesive which is cleaned by reverse flow backflushing.
Several systems have been proposed for the filtering of impurities from fluids, including viscous liquids such as hot melt adhesives. In most systems of this general type, unfiltered liquid is pumped into a filter which is carried within a manifold, vessel or other housing structure. The unfiltered liquid flows either from the outside surface of the filter inwardly to its core, or vice versa, and then the filtered liquid is collected and discharged through an outlet in the housing structure for further use. Eventually the filter begins to clog with collected impurities which must be removed to retain the desired filtering capacity.
In some systems, no provision is made for removing contaminants from the filter while it remains within the housing structure. This requires the system pump to be shut down and the filter removed for cleaning exteriorly of the housing structure or for replacement with a new filter. The downtime associated with removal, cleaning and/or replacement of a filter is particularly disadvantageous in filtering hot melt adhesives or similar materials wherein temperature of the material must be maintained within certain ranges. For example, if hot melt adhesive is allowed to cool as a result of excessive downtime of the filtering system, it becomes extremely viscous and difficult to dispense until the temperature is returned to normal operating levels.
Other filtering systems remove contaminants from the filter by a backflush operation in which contaminants are removed from the filter without removing it from the housing structure. The backflush fluid is often introduced into the filter in the opposite or reverse direction from the direction of flow of the liquid to be filtered, and dislodges contaminants from the filter for removal through a drain. Unfortunately, many filtering systems are characterized by relatively complex valving arrangements and/or other flow control devices to convert from the filtering operation to the backflush operation. In order to clean the filter by backflushing, such filtering systems employ one set of valves to shut off the flow of unfiltered fluid to the filter, and another set of valves or other flow control devices to introduce the backflush fluid into the filter. These systems are not only relatively costly to construct and maintain, but often make access to the filter difficult for replacement or external cleaning.